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The Niwa National Climate Centre is forecasting a warmer and drier than average spring in the South, but be prepared for fog and frosts.
Meteorologist Ben Noll said temperatures in Otago and Southland were ''equally likely'' to be above average or near average between September and November.
Rainfall totals, soil moisture levels and river flows were ''equally likely'' to be near normal or below normal.
He said the consensus from international models was for the tropical Pacific to transition toward El Nino over the next three-month period.
''The probability for El Nino conditions being established will increase as we reach into and beyond the southern hemisphere summer, with a 78% chance for El Nino conditions over the March-May 2019 period.
''Indications are that the event - if it eventuates - will not be in the strong category.
In other words, the upcoming El Nino event, should it come to fruition, is not expected to be of a similar intensity to what was experienced during 2015-16, 1997-98, or 1982-83 and therefore different impacts are expected.''
During the next three months, atmospheric circulation around New Zealand was forecast to be characterised by higher pressure than normal over the South Island, he said.
The circulation pattern may be associated with cold nights and mornings, as well as frosts and fog, especially early in the spring season, he said.
However, sea surface temperatures warmed around New Zealand during the month of August, which may help lessen ''the sting'' of colder air masses as they pushed toward New Zealand during the spring season.